1. Field of the Invention
This invention relates generally to multiple cartridge magazine handling in automated data storage libraries and, more specifically, to a robotic picker for handling and transporting both individual data storage cartridges and detachable multiple cartridge magazines.
2. Discussion of Related Art
Numerous business applications require very large data stores for storing information used in large business databases. Database storage requirements often exceed 1,000 GB and data storage costs tend to relegate such large databases to low-cost magnetic tape stores. Unfortunately, such low-cost stores cannot provide efficient data access speed and reliability. Efficient access is particularly important in business applications requiring frequent updates to the database. Magnetic tape storage is particularly inefficient for frequent database updates. For example, even after a tape cartridge is loaded onto a tape drive, access to data in the mounted tape is still substantially slower than access to data stored on Direct Storage Access Devices (DASDs) or optical disks. This problem is substantially exacerbated by the additional delays associated with manually locating and mounting a requested magnetic tape cartridge.
Automated data storage libraries offer some improvements in speed and reliability for data storage and retrieval from magnetic tape cartridges and other data storage media (DSM cartridges) such as optical media. Advances in magnetic tape cartridge technology have also enhanced the efficiency of automated tape cartridge libraries.
Access time and reliability are improved by the robotic or automatic management of the storage and retrieval of tape cartridges. The typical automated cartridge library known in the art includes a plurality of bins or storage slots for passively storing resident DSM cartridges such as tape cartridges, a robotic picker mechanism, and one or more Peripheral Data Storage Device (PDSD) bays or drive slots. The robotic picker mechanism operates on command to transfer a DSM cartridge between a storage slot and a drive slot for mounting on a PDSD. This sort of automated data storage library offers many operational benefits, including greater DSM cartridge mount reliability, improved uniformity of request-to-mount time, and improved off-shift availability. Such libraries often include a manual port for inserting and removing DSMs, such as tape cartridges, from the library.
Automated data storage libraries suffer generally from one or more specific shortcomings. Although the mechanical automation improves the performance of very large databases, an automated library is disadvantaged in terms of necessary floor space, data storage capacity, data access and retrieval delays and the frequently serviced mechanisms necessary for automatic operation. Practitioners in the art have suggested various improvements to the automatic data storage library, particularly improved PDSD mounting operations and improved DSM cartridge transfer into and out of the library. These operations require improved DSM cartridge mounting and handling procedures and improved robotic picker mechanical design.
For instance, in U.S. Pat. No. 5,065,265, Michel A. Pierrat discloses an improved storage carrousel having a plurality of rotatable sub-carrousels for use in an automatic data storage library. Pierrat teaches a design for a carrousel and robotic arm for use in the library, thereby increasing a storage capacity by 30-40% without increasing the physical size of the library. His robotic picker design is smaller and lighter because his carrousel design results in less weight carried by the arm.
In Japanese patent 59-77670, Katsuyuki Obata et al disclose a new gear and cam arrangement for use in a tape cassette magazine loader and unloader. With their design, the same mechanism performs both loading and unloading, distinguishing between the two by merely switching cams. Obata et al teach a method for operating their cartridge loader/unloader with a single motor, thereby reducing the mechanism size and complexity. However, Obata et al do not consider or suggest application of their invention to an automatic data storage library, limiting their teachings to simple tape cassette magazine handlers.
More recently, in a disclosure entitled "Camera and Gripper Assembly For an Automated Storage Library", filed on Oct. 15, 1991 as patent application Ser. No. 07/776,945 now issued as U.S. Pat. No. 5,237,468, J. F. Ellis discloses an optical gripper designed for mounting at the end of a robotic arm. Ellis's gripper assembly permits pick-before-place cartridge operations to be performed with a single camera and two grippers, thereby substantially improving automatic loading and unloading efficiency. This U.S. Pat. No. 5,237,468 is entirely incorporated herein by this reference.
Practitioners have introduced the Automatic Cartridge Loader (ACL) for use in improving the efficiency of PDSD mounting procedures. The ACL is a "stacker" or serial DSM cartridge loader, as is well-known. Manufacturers such as Hitachi, IBM, HDS and Fujitsu produce automated data storage libraries including the ACL feature. All such ACLs are serial access devices.
An analogous random access DSM cartridge loader for use in automated data storage libraries is unknown in the art, perhaps because the "picker" and library DSM storage slots operate as a single large random access DSM cartridge loader. The travel time between the DSM storage slots and the input-output ports or PDSDs occupies 40-60% of the total DSM cartridge transport time. Automated libraries known in the art provide grippers having capacity to transport, at most, two DSM cartridges at a time. Most libraries that use ACLs to cache five to ten DSM cartridges at a time require that the ACL be loaded or unloaded by a DSM cartridge gripper at the rate of one DSM per gripper cycle. The Odetics intermediate library system product uses a DSM magazine to load and unload cartridges from the library, but such transfers are exclusively manual operations. The ACLs known in the art are all sequential DSM magazines that provide no means for random DSM cartridge access.
In a disclosure entitled "Multi-Media-Type Automatic Libraries", filed on Jan. 3, 1992 as patent application Ser. No. 07/816,590, J. E. Kulakowski, et al disclose a system for handling diverse and incompatible data storage media (DSM cartridges) within a single automated data storage library. This patent application Ser. No. 07/816,590 is entirely incorporated herein by this reference. Kulakowski et al teach a new library design that includes a DSM cartridge storage array having a plurality of storage receptacles for removably receiving cartridge-holding magazines. Each magazine stores a plurality of DSM cartridges in individual slots. These slots are arranged to open into the DSM transport system so that the magazines held in the storage receptacles constitute a series of DSM cartridge storage arrays for different types of DSM cartridges. Kulakowski et al teach inserting and removing DSM cartridges from the library either by manually passing individual DSM cartridges through an exterior port or by removing and inserting the entire magazine manually. Kulakowski et al do not consider dual-purpose means for automatically transporting DSM cartridges individually or in magazines internally within the automated library. Their invention is limited to a technique for loading and unloading incompatible DSM cartridge types and their magazine arrangement is limited to the purpose of segregating such incompatible DSM cartridge types.
Techniques for bulk transport of DSM cartridges and transport of trays of several cartridges each is known in the art, as discussed in the above-cited Kulakowski et al patent application. However, a method for randomly loading one of a plurality of DSMs held in a DSM magazine is neither taught nor suggested in the existing art.
There remains a clearly felt need in the art for improved data storage capacity and data access efficiency in automated data storage libraries in general and through improved automated DSM cartridge handlers or "pickers" specifically. The related problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.